The present invention relates generally to the field of circuit breakers, and more particularly to a ring tongue lug retainer for a molded case circuit breaker.
In general the function of a circuit breaker is to electrically engage and disengage a selected circuit from an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.
A typical industrial circuit breaker will have a continuous current rating ranging from as low as 15 amps to as high as several thousand amps. The tripping mechanism for the breaker usually consists of a thermal overload release and a magnetic short circuit release. The thermal overload release operates by means of a bimetallic element, in which current flowing through the conducting path of a circuit breaker generates heat in the bi-metal element, which causes the bi-metal to deflect and trip the breaker. The heat generated in the bi-metal is a function of the amount of current flowing through the bi-metal as well as the period of time that that current is flowing. For a given range of current ratings, the bi-metal cross-section and related elements are specifically selected for such current range resulting in a number of different current ranges for each circuit breaker. Electronic trip units are also used in some applications.
In the event of current levels above the normal operating level of the thermal overload release, it is desirable to trip the breaker without any intentional delay, as in the case of a short circuit in the protected circuit, therefore, an electromagnetic trip element is generally used. In a short circuit condition, the higher amount of current flowing through the circuit breaker activates a magnetic release which trips the breaker in a much faster time than occurs with the bi-metal heating. It is desirable to tune the magnetic trip elements so that the magnetic trip unit trips at lower short circuit currents at a lower continuous current rating and trips at a higher short circuit current at a higher continuous current rating. This matches the current tripping performance of the breaker with the typical equipment present downstream of the breaker on the load side of the circuit breaker. Again, electronic trip units can also be used.
Ratings of circuit breakers are continually increasing due to market driven requirements for space saving electrical equipment. As the ampere rating for a given circuit breaker frame size increases, space for wiring lugs within that circuit breaker becomes a premium. Lug size for attaching the various wires and cables is primarily driven by the wiring cable dimensions as defined in the National Electric Code or other country specific wiring standards or practices. Although this problem exists for all circuit breakers, it is especially acute for circuit breakers in the 100 amp to 125 amp range.
Existing techniques for connection of the various wires and cables relative to the circuit breaker is done with a lug mounted in the circuit breaker. A wire or cable is inserted into the lug and a screw is turned and engages the wire typically with a crushing or squashing of the wires as the screw is turned down in the lug. The screw may have a plate fixed at its bottom with prongs that engage the cable or wire. The lug is typically mounted in the circuit breaker either by additional hardware such as screws or rivets or by a series of tabs and notches configured in either the housing of the circuit breaker or the lug or both. In some instances, a wire or cable has a ring tongue connector or the like mounted by solder or crimping as a terminator for the wire end. The ring tongue connector is then bolted or screwed to the line and load bus conductors of the circuit breaker. In other instances the ring tongue is simply squeezed by the lug screw as the lug screw is turned into the wire lug, usually with less than 100% mechanical or electrical contact being made between the ring tongue connector and the electrical bus conductor.
The existing wiring connections require either additional hardware, special manufacturing techniques for the wire lug and circuit breaker housing, or the electrical connection does not utilize the entire portion of the ring tongue terminator which is engaged by the wire lug of the circuit breaker.
Thus, there is a need for a positive ring tongue securing apparatus that provides maximum annular contact of the ring tongue and bus bar conductor in a circuit breaker. There is also a need for a lug retainer that does not require separate hardware to hold the lug in place. There is also a need for a circuit breaker that allows the wire lug to be easily mounted to the bus conductor of the circuit breaker during manufacturing or field repair.
The present invention provides a ring tongue lug retainer in a circuit breaker with the circuit breaker having a line bus conductor and a load bus conductor, wherein electrical conductors are connected to the line and load bus conductors. The ring tongue lug retainer comprises a lug body having a throughbore defining at least two interior walls and a threaded screw hole aligned perpendicular to and in communication with the throughbore. A thread portion in each interior wall of the lug body may be provided to engage the binding screw configured to threadingly engage the screw hole and the lug body. The binding screw has a ring tongue protrusion configured to engage a ring tongue terminal of the electrical conductors. The ring tongue protrusion can be one selected from a group comprising a cylinder with a round end, a trunkated cone, a cylinder with a pointed end and a cylinder with a flat end and spherical knob. Another embodiment of the ring tongue lug retainer includes a slot extending into the lug body and in communication with the throughbore. The slot can be configured to engage one of the line bus conductor and load bus conductor and the slot may extend through the lug body.
The present invention further provides a molded case circuit breaker comprising a molded housing, a line bus conductor and a load bus conductor inserted in the housing with the first contact coupled to the line bus conductor and a second contact coupled to the load bus conductor. An operating mechanism having a pivoting member movable between an xe2x80x9cONxe2x80x9d position, and xe2x80x9cOFFxe2x80x9d position and a xe2x80x9cTRIPPEDxe2x80x9d position, with the pivoting member coupled to the second contact. A trip unit coupled to the second contact and the load bus conductor is selectively in operative contact with the operating mechanism. An electric arc extinguishing apparatus is mounted in the housing and is positioned in confronting relation with the first and second contacts, a ring tongue lug retainer is mounted in the circuit breaker housing at one of the load and line terminals. The ring tongue lug retainer comprises a lug body having a throughbore defining at least two interior walls and a threaded screw hole aligned perpendicular to and in communication with the throughbore. A thread portion in each interior wall of the lug body may be provided and a binding screw configured to threadingly engage the screw hole and the lug body. The binding screw has a ring tongue protrusion configured to engage a terminal, such as a ring tongue, on the electrical conductors.
The present invention also provides a circuit breaker comprising a molded housing including a base, with a means for connecting a load to the circuit breaker mounted in the housing and a means for connecting an electrical line to the circuit breaker mounted in the housing. A means for coupling electrically to the means for connecting an electrical line is also provided. A movable means for contacting the means for connecting an electrical line to a means for operating is mounted in the housing coupled with the means for operating having a pivoting member movable between an xe2x80x9cONxe2x80x9d position, an xe2x80x9cOFFxe2x80x9d position and a xe2x80x9cTRIPPEDxe2x80x9d position. The pivoting member is coupled to the movable means for contacting and with the means for operating. A means for tripping is coupled to the movable means for contacting and the means for connecting a load with the means for operating wherein the means for tripping includes a means for releasing under short circuit condition and a means for releasing under an overload condition. A means for extinguishing an electrical arc is mounted in the housing with a movable means for contacting extended into the means for extinguishing. A means for retaining having a throughbore and coupled to one of the means for connecting a load and the means for connecting an electrical line is also provided. In another embodiment, the means for retaining includes the slot in communication with the throughbore.